Wireless links have an ever increasing demand on the data rate of data communicated through the wireless links. With more and more people using broadband internet this demand is only projected to grow further. Some of the application use cases include high capacity terrestrial wireless links to bridge fiber connections across obstacles, and high capacity satellite uplinks.
MIMO (multiple-input, multiple-output) wireless links using spatial multiplexing can be used to scale capacity further once higher order modulation becomes impractical and time/frequency/polarization multiplexing degrees of freedoms have been exhausted. However, a solution is needed that supports spatial multiplexing over several GHz of RF (radio frequency) bandwidth, especially in mm (millimeter)-wave bands.
Traditional spatial multiplexing architectures digitize signal streams from multiple antennas and perform spatial multiplexing processing in digital baseband. This has limitations when the signal bandwidth is several GHz. That is, high speed digital interconnects and digitizers are needed that are power hungry. Further, since processing needs to be done at high symbol rates digital implementations are heavily pipelined resulting in high latency.
Further, attempts at analog spatial multiplexing architectures also have limitations. That is, these architectures suffer from a bandwidth that is not wide enough, and inter-stream interference cancellation can only be guaranteed for a few 100's of MHz. Further, these previous attempts at analog spatial multiplexing architectures cannot handle large delay spreads (several multiples of carrier wavelengths) experienced in air to ground or satellite to ground links. Further, the performance degrades if multiple analog front ends have widely different frequency responses. Further, performance cannot be guaranteed under atmospheric scintillation experienced over long range mm-wave links.
It is desirable to have methods apparatuses, and systems for broadband analog spatial multiplexing over broad bandwidth (several GHz).